1. Field of the Invention
The present invention relates to a mixing or blending arrangement and more particularly, to a mixing apparatus used, for example, for dispersing and mixing coating agents such as calcium carbonate, kaolin and the like into water as a solvent in a paper manufacturing process, or for dispering and mixing a granular component such as dextrose and the like into distilled water as a solvent in a manufacturing process of Ringer's solution, or for dispersing and mixing powdered or granular materials into solvents in other food article manufacturing processes.
2. Prior Art
Conventionally, a mixing apparatus of the type described above used an arrangement in which a downwardly directed pipe supplying the powdered or granular materials (referred to merely as granular materials hereinafter) positioned above the liquid surface in the mixing tank containing the solvent discharges the granular materials to be mixed (or dissolved) onto the liquid surface of the solvent for subsequent stirring.
The prior art mixing apparatus described above, however, has the disadvantage that the granular material discharged from the supply pipe tend to concentrate in the upper portion of the mixing tank during agitation before they dissolve into the solvent. This results not only in an unsanitary appearance, but in soiling of the peripheral portions of the mixing tank or formation of undissolved powder lumps (flocs) by the granular materials floating on the surface of the solvent. Accordingly, a long time is required for the removal of such flocs, with a concomitant loss of energy. There is also an undesirable tendency for wet solids to adhere to the periphey of the supply port of the granular material supply pipe. Moreover, for an efficient dispersion of the granular materials into the solvent, it is necessary to increase the surface area of the granular materials for better contact with the solvent. Therefore, the granular materials must be discharged into the solvent little by little in limited small amounts, which is another undesirable feature of such an apparatus.
In order to eliminate the disadvantages described so far, for example, the concentration or non-uniform mixing of the granular materials, there has been proposed, in the Japanese Patent Publication Sho No. 43 (1968)-6260, a method of adding and mixing a fine powdered material into a liquid in which a porous plate or dispersing unit including filters is provided in a vacuum-resistant mixing apparatus. A fine powdered material supply port is opened in the lower part of the dispersing unit, while the liquid is supplied to the upper portion of the porous plate, and the fine powdered material is drawn into the liquid through the fine powdered material supply port, with the interior of the mixing apparatus main body maintained under a vacuum for dispersion and mixing.
In the arrangement described above, the fine powdered material is drawn from the lower part of the dispersing unit to the upper part by air suction created by a vacuum pump. This results in increased air flow, causing deterioration in quality depending on the physical properties of the fine powdered material, and accordingly, the method as described so far has the disadvantage that it is not suitable for general purposes. Moreover, in the arrangement described above it is necessary to provide a special means (for example, installation of a baffle plate within the apparatus main body or mounting of a collecting unit on the vacuum system piping) to prevent the fine powdered material from entering the interior of the vacuum pump through the vacuum system piping. Furthermore, since the interior of the mixing apparatus is at a reduced pressure, one must provide a sealed construction to avoid any leakage of air from the main body of the mixing apparatus. In addition, since the fine powdered material is drawn into the interior of the main body of the mixing apparatus by the air suction created by the vacuum pump, it may be possible to provide a plurality of mixing apparatuses for dispersion mixing of fine powdered material; but in such a case, complicated piping is required, with a consequent increase in cost. Moreover, there is the disadvantage that transporting the fine powdered material over a long distance for its mixing in the main body of the mixing apparatus requires a large-sized vacuum pump and system which is uneconomical in practice.